1. Field of the Invention
The present invention relates to a technique for correcting distortion of an image of a prescribed subject obtained when the prescribed subject is photographed.
2. Description of the Related Art
When information (characters, figures and the like) written on a surface of a subject which can transform, such as a paper medium (for example, notebook and a document) is photographed and recorded as an image, an image reflected by the original shape of the subject can be obtained, when the photographed image is subjected to a trapezoidal distortion correction. In the following description, the term of “subject” is sometimes referred to as a “manuscript”, but the “manuscript” means the paper medium itself to be photographed, but does not mean drafts or draft articles.
When a photographed manuscript includes three-dimensional distortions (a distortion due to a curved manuscript and local distortions due to the irregularly curved manuscript), and if the trapezoidal distortion correction is made only to the manuscript image so as to produce a corrected manuscript image, then such three-dimensional distortions will be more emphasized in the corrected manuscript image.
The technique for solving the above problem has been proposed, for example, by Japanese Unexamined Patent Publication No. 2010-130181. The technique detects a vanishing point, that is, a vertical vanishing point in the vertical direction perpendicular to text lines in the manuscript and a horizontal vanishing point in the horizontal direction perpendicular to the vertical direction of the manuscript in the manuscript image, respectively. Then, a grid is set in the manuscript image, which grid consists of plural vertical lines drawn on the basis of the vertical vanishing point and plural horizontal lines drawn on the basis of the horizontal vanishing point, whereby plural unit square areas are defined in the manuscript image by the grid. Then, a correcting process is performed on the plural unit square areas defined in the manuscript image to transform the shape of each of the unit square areas into a rectangle shape, whereby a corrected image is reproduced, which is substantially in the same state as the photographed manuscript representing character information with no three-dimensional distortion included therein.